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SubjectRe: [PATCH 1/2] xen/blkback: turn the cache purge LRU interval into a parameter
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On 15.10.20 16:24, Roger Pau Monne wrote:
> Assume that reads and writes to the variable will be atomic. The worse
> that could happen is that one of the LRU intervals is not calculated
> properly if a partially written value is read, but that would only be
> a transient issue.
>
> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> ---
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> Cc: Jens Axboe <axboe@kernel.dk>
> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> Cc: SeongJae Park <sjpark@amazon.de>
> Cc: xen-devel@lists.xenproject.org
> Cc: linux-block@vger.kernel.org
> Cc: J. Roeleveld <joost@antarean.org>
> Cc: Jürgen Groß <jgross@suse.com>
> ---
> Documentation/ABI/testing/sysfs-driver-xen-blkback | 10 ++++++++++
> drivers/block/xen-blkback/blkback.c | 9 ++++++---
> 2 files changed, 16 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/ABI/testing/sysfs-driver-xen-blkback b/Documentation/ABI/testing/sysfs-driver-xen-blkback
> index ecb7942ff146..776f25d335ca 100644
> --- a/Documentation/ABI/testing/sysfs-driver-xen-blkback
> +++ b/Documentation/ABI/testing/sysfs-driver-xen-blkback
> @@ -35,3 +35,13 @@ Description:
> controls the duration in milliseconds that blkback will not
> cache any page not backed by a grant mapping.
> The default is 10ms.
> +
> +What: /sys/module/xen_blkback/parameters/lru_internval

s/lru_internval/lru_interval/

> +Date: October 2020
> +KernelVersion: 5.10
> +Contact: Roger Pau Monné <roger.pau@citrix.com>
> +Description:
> + The LRU mechanism to clean the lists of persistent grants needs
> + to be executed periodically. This parameter controls the time
> + interval between consecutive executions of the purge mechanism
> + is set in ms.
> diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
> index adfc9352351d..6ad9b76fdb2b 100644
> --- a/drivers/block/xen-blkback/blkback.c
> +++ b/drivers/block/xen-blkback/blkback.c
> @@ -117,7 +117,10 @@ MODULE_PARM_DESC(max_ring_page_order, "Maximum order of pages to be used for the
> * be executed periodically. The time interval between consecutive executions
> * of the purge mechanism is set in ms.
> */
> -#define LRU_INTERVAL 100
> +static unsigned int lru_interval = 100;
> +module_param_named(lru_interval, lru_interval, uint, 0644);
> +MODULE_PARM_DESC(lru_internval,

s/lru_internval/lru_interval/

> + "Time interval between consecutive executions of the cache purge mechanism (in ms)");
>
> /*
> * When the persistent grants list is full we will remove unused grants
> @@ -620,7 +623,7 @@ int xen_blkif_schedule(void *arg)
> if (unlikely(vbd->size != vbd_sz(vbd)))
> xen_vbd_resize(blkif);
>
> - timeout = msecs_to_jiffies(LRU_INTERVAL);
> + timeout = msecs_to_jiffies(lru_interval);
>
> timeout = wait_event_interruptible_timeout(
> ring->wq,
> @@ -650,7 +653,7 @@ int xen_blkif_schedule(void *arg)
> if (blkif->vbd.feature_gnt_persistent &&
> time_after(jiffies, ring->next_lru)) {
> purge_persistent_gnt(ring);
> - ring->next_lru = jiffies + msecs_to_jiffies(LRU_INTERVAL);
> + ring->next_lru = jiffies + msecs_to_jiffies(lru_interval);
> }
>
> /* Shrink the free pages pool if it is too large. */
>


Juergen

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